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Title: A study by electron microscopy of the development of the secondary phloem of ash (Fraxinus excelsior)
Author: Hamzah, Samsidar
ISNI:       0000 0001 3529 1440
Awarding Body: University of London
Current Institution: Royal Holloway, University of London
Date of Award: 1977
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The ontogenetic development of the secondary sieve elements in ash, Fraxinus excelsior is traced by using mainly conventional electron microscopy. In addition, negative staining of the exudate and light microscopy have also been used. No major differences from the established trends have been observed in the differentiation of these sieve elements. There is evidence that the P-protein in the sieve elements originates from helical polysomes found scattered in the dense cytoplasm of young sieve elements. These polysomes also give the appearance of having been derived from rough ER cisternae. Reorganisation of the fibrillar P-protein into the tubular form also seems to take place in the larger P-protein bodies. In negatively-stained preparations, a suggestion of a tightening of the double helix of the P-protein fibrils is discernible. This reorganisation is however not consistent. The usual banding of the fibrillar P-protein is prominent. Most of the mature sieve plates show occluded pores either callosed or not. The P-protein frequently appears to fray out on the downstream side and sometimes on the upstream side as well. This has a bearing on the nature of functioning sieve plates and does not seem to be due to artifacts. Empty spaces which represent probably a peculiar artifact are observed immediately above most of the mature sieve plates. P-protein seems to pile above these "barrier" spaces while the sieve plates remain occluded with P-protein. Other formations of peculiar interest are the plasmalemmal invaginations ("blebs") found both in the sieve elements and in the parenchyma cells. In the sieve elements, their formation seems to be in an endocytic (pinocytotic) direction. In terms of the sieve tubes, these "blebs" have a possible significance in the uptake of solutes and ions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Botany